Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-10-11
2002-07-16
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S193000, C525S232000, C525S238000, C525S240000, C525S241000
Reexamination Certificate
active
06420483
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for preparing impact-modified plastics, and also to an impact-modified plastic obtainable using the process.
Impact-modified plastics have improved mechanical properties, making them particularly suitable for many applications, for example consumer articles. These particular properties are achieved through the structure of these plastics, in which elastomer domains, for example rubber domains, have been embedded in a matrix made from the thermoplastic. The presence of more than one phase in these impact-modified plastics, and therefore also their domain structure, arises due to their build-up from different polymeric components which are immiscible, or only partially miscible, with one another. Their impact-strength is a result of absorbing more energy during deformation before fracture occurs. This energy is used in forming microcavities or for inducing sliding effects within the matrix polymer chains. The presence of more than one phase is therefore a necessary precondition for achieving high impact strengths.
Other factors which apply are as follows:
1. The two chemically different polymeric components generally form a stable dispersion with a defined particle size, showing only little phase separation during processing and without any tendency to homogenize with formation of a macromolecular solution on exposure to relatively intense heat.
2. There must be some coupling present between the elastomer particles and the matrix, that is to say the phase boundaries must be capable of transferring forces.
The most effective coupling at the elastomer particle interfaces is achieved by graft copolymerization. The process here is generally to take a rubber and then to graft a copolymer onto this by polymerizing with a monomer mixture.
DESCRIPTION OF THE RELATED ART INCLUDING INFORMATION DISCLOSURE UNDER 37 CFR 1.97 and 198.
DE-A-2 910 168 discloses stable, flowable dispersions of rubbers in the form of discrete particles of average diameter from 100 to 3000 nm in organic liquids in which the rubber present is from 1 to 20% by weight (based on the entire dispersion) of a crosslinked diene rubber, and from 0 to 20% by weight of water in the form of a water-in-oil emulsion is present. As continuous organic phase they comprise from 99 to 66% by weight of C
1
-C
10
-alkyl acrylates or alkyl methacrylates, methyl methacrylate, ethyl acrylate or n-hexylacrylate. As an alternative, they may also comprise, as liquid phase, a mixture of from 85 to 50% by weight of styrene or x-methylstyrene and from 15 to 50% by weight of acrylonitrile, methacrylonitrile or C
1
-C
6
-alkyl acrylates or, respectively, alkyl methacrylates, such as methyl methacrylate, ethyl acrylate or n-hexyl acrylate. A further alternative proposed for the continuous organic phase is a mixture of from 85 to 50% by weight of C
1
-C
10
-alkyl acrylate or, respectively, alkyl methacrylate and from 15 to 50% by weight of acrylontrile, methacrylonitrile or styrene. The continuous organic phase may in each case comprise up to 60% by weight of an admixed liquid hydrocarbon. Aqueous emulsions of crosslinked, rubbery diene polymers are dispersed in certain organic liquids, and the result is dispersion of the diene polymers in the form of swollen particles. The water of the initial emulsion is likewise present in dispersed form in the organic liquid, as a water-in-oil emulsion. If required, the water may be removed by selectively breaking the water-in-oil emulsion and separating off the water. However, for most applications of the organic rubber dispersions there is no requirement to separate off the water, but it must be in stable dispersed form and not separate out as a distinct phase.
DE-A-4 440 676 describes a process for preparing rubber molding compositions, and also rubber-modified molding compositions prepared by the process. Here, a first stage polymerizes a mixture which comprises at least one alkyl acrylate or alkyl methacrylate, a first monomer having two or more double bonds and, if desired, one or more second monomers, to give a rubber, preferably using free radicals. A second stage dissolves, or swells, the resultant rubber in one or more third monomers to give a second mixture, if desired with addition of a solvent, and a third stage polymerizes the second mixture formed by the dissolution or swelling, to give the rubber-modified molding composition. Examples of first monomers are allyl methacrylate, butanediol diacrylate, divinylbenzene, triallyl cyanurate and dihydrodicyclopentadienyl acrylate, and the latter is preferred. The dienes used therefore comprise compounds with isolated double bond. Examples given for the second monomers are styrene, acrylonitrile, acrylic acid, methacrylic acid, and also derivatives of the two latter monomers.
DE-A-2 400 659 describes a process for preparing rubber-modified resins. Here, an alkadiene rubber, which has been grafted with monovinylidene-aromatic monomers and with alkene nitrile monomers, is dispersed into a hot melt of a base copolymer composition of monovinylidene-aromatic monomers and alkene nitrile monomers. The impact-modified plastic is therefore prepared through a physical mixing procedure. The grafting required for adequate force-transfer between polymer matrix and rubber has to be carried out in a separate step.
U.S. Pat. No. 3,957,912 describes a process for preparing an acrylonitrile-butadiene-styrene plastic. Here, an alkyl-diene rubber is first polymerized with styrene and/or acrylonitrile monomers by emulsion polymerization, to give a grafted rubber. Styrene and/or acrylonitrile are then added to this rubber, as is at least one solvent for the styrene-acrylonitrile copolymers. The rubber is taken up in the solvent, the water is separated off, and the mixture of rubber, solvent and monomer is polymerized. The transfer of the rubber into the solvent makes this process complicated to carry out.
U.S. Pat. No. 3,903,199 and U.S. Pat. No. 3,903,200 describe processes for preparing acrylonitrile-butadiene-styrene polymers. Here, particles of a first grafted rubber are dispersed in a mixture of a monovinylidene-aromatic monomer and an alkene nitrile monomer. The process consists in either first partially polymerizing the mixture and then adding particles of a second grafted rubber and polymerizing the matrix to completion or in adding the particles of the second grafted rubber directly to the mixture of the monomers and polymerizing the matrix to completion. In both cases the plastic obtained has bimodal size distribution of the rubber particles.
Due to the particular properties of impact-modified plastics, their wide application and their resultant economic importance, there is a constant requirement for new and improved plastics of this type.
It is an object of the present invention, therefore, to provide a process for preparing impact-modified plastics, and also an impact-modified plastic obtainable by this process.
BRIEF SUMMARY OF THE INVENTION
We have found that this object is achieved by means of a process for preparing an impact-modified plastic, where
in a first step, particles of a crosslinked rubber are produced from a first monomer mixture which has at least 50% by weight of conjugated diene compounds,
the rubber particles are added to a second monomer mixture which has at least 85% by weight, preferably at least 90% by weight, in particular at least 98% by weight, of styrene, and
the monomers of the second monomer mixture are polymerized.
DETAILED DESCRIPTION OF THE INVENTION
The first step of the process produces a rubber in particle form, onto which the monomers of the second monomer mixture are then grafted. This gives effective phase coupling at the interfaces between the elastomer particles and the surrounding polymer matrix. No separate step is required to polymerize-on the graft shell. The high proportion of conjugated diene compounds in the rubber gives better resistance to mechanical effects, and this is also true at relatively low temperatures. There is no requirement for the dispersi
Gausepohl Hermann
Güntherberg Norbert
Mc Kee Graham Edmund
Niessner Norbert
BASF - Aktiengesellschaft
Keil & Weinkauf
Nutter Nathan M.
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